2.4 Cell proliferation assay
Cell proliferation was detected using a Cell Counting Kit-8 (CCK-8; Biosharp; Cat#BS350A). HUVECs and HDF cells were separately seeded 2×103/well in 96-well plates. The cells were allowed to adhere for 12 h at 37 °C in 5% CO2. After 12 h, the medium was removed and replaced with 100 μL of FGF2 or PEG-FGF2 conjugates for 24 h before addition of CCK-8 solution (10 μL) to each sample. The absorbance was measured at 450 nm using a microplate reader (Molecular Devices, USA). Cell proliferation assays were performed in triplicate.